The present invention relates to a charged particle beam irradiation apparatus for irradiating a target object with a charged particle beam for medical treatment of cancer, bactericide in foods, improvement of plant breeding, non-destructive inspection of machines, and the invention relates especially to a charged particle beam irradiation apparatus which is capable of reducing power consumption.
In using a charged particle beam (hereafter, referred to simply as a beam) of high energy, which is generated by an accelerator, for medical treatment of cancer, etc., there is a method in which the diseased part is scanned with a charged particle beam, and another method in which the diameter of the charged particle beam is enlarged to make its dose distribution uniform and in which the enlarged charged particle beam is then shaped by using a collimator to fit to the shape of the target object, that is, the diseased part.
In the above two irradiation methods, the method of scanning a target with a charged particle beam has been implemented using the following methods: that is, the wobbler method of scanning a target with a charged particle beam, the raster scanning method of scanning a target with a charged particle beam in a zigzag manner, and the pixel scanning method of irradiating a target in a pixel state manner.
In the above scanning methods, two electromagnets are used, and the beam deflecting directions of the first and second electromagnets are set perpendicular to each other. Also, a plane perpendicular to the axial direction of the beam is scanned by the beam deflected by these electromagnets.
FIG. 7 is a schematic diagram of the composition of a conventional charged particle beam irradiation apparatus in which a beam irradiation unit using the wobbler method is installed in a rotation gantry. A charged particle beam emitted from an accelerator (not shown in the figure) is inputted into the rotation gantry and outputted from an irradiation nozzle 40. The diseased part is circularly scanned with the charged particle beam output from the irradiation nozzle 40 by two scanning electromagnets 100 and 110. The scanning electromagnet 100 deflects the beam in the X direction, and the scanning electromagnet 110 deflects the beam in the Y direction. By changing the amount of deflection of the beam in each scanning electromagnet with time, circular scanning can be performed.
In the above-mentioned conventional technique, it is necessary to set the gap between magnetic poles of the scanning electromagnet 110 wide enough so that the beam deflected by the scanning electromagnet 100 is prevented from striking the magnetic poles of the scanning electromagnet 110, since the deflection direction in the scanning electromagnet 100 is parallel to the magnetic poles of the scanning electromagnet 110. Widening the gap between the magnetic poles causes a problem in that a larger current is required in order to generate a magnetic field having the necessary strength, which increases the power consumption of the irradiation apparatus.